In-situ electrochemical and operando Raman techniques to investigate the effect of porosity in different carbon electrodes in organic electrolyte supercapacitors

The analyzes of micro-, meso- and macro-porous carbon electrodes in a symmetrical supercapacitor filled with a 1.0 M TEABF(4) EC-DMC electrolyte were reported in this work. The activated carbon (AC), multi-walled carbon nanotubes, and graphite materials were studied. The results indicate AC is the best electrode material for the application with high specific capacitance and energy. The Raman operando analyzes of AC show that the D- and G- bands shift their positions and intensities. The cause of this phenomenon is the electrostatic ionic adsorption inside very narrow pores, affecting the vibrational mode and the work function of the material, resulting in the shift of the Fermi level of the material. For mesoporous carbon, this phenomenon is much less pronounced. In principle, graphite has enough specific capacitance for competitive application. However, its overall surface area is reduced. Graphite's Raman operando analyzes revealed the BF4- insertion into graphene layers. The G-band splits while the in-situ electrochemical data support a capacitance with three orders of magnitude higher than expected for a purely electrostatic adsorption process on graphite. Overall, this fundamental study evidences that in-situ electrochemistry and Raman spectroscopy combined could offer important information on the energy storage process for supercapacitors.

Automated summary

This work presents the analysis of micro-, meso-, and macro-porous carbon electrodes in a symmetrical supercapacitor filled with a 1.0 M TEABF(4) EC-DMC electrolyte. The results show that activated carbon (AC) is the most suitable electrode material due to its high specific capacitance and energy. Raman spectroscopy analysis reveals that AC experiences shifts in the D- and G-bands due to electrostatic ionic adsorption in narrow pores. Graphite, though having enough specific capacitance for competitive application, has a reduced overall surface area. Graphite's Raman analysis shows BF4- insertion into graphene layers. Overall, this study demonstrates that in-situ electrochemistry and Raman spectroscopy combined can provide important information on the energy storage process in supercapacitors.